The present invention relates to a plasma processing method.
Plasma processing apparatuses constituted by employing various types of plasma sources have been proposed in the area of semiconductor manufacturing apparatuses in the prior art. They include a plasma processing apparatus that is capable of performing plasma processing on an object such as a substrate by forming an electric field between an upper electrode and a lower electrode provided facing opposite each other within a processing chamber and by generating plasma from a processing gas introduced into the processing chamber with the electric field.
The plasma processing apparatuses above also include the so-called magnetic field assist type plasma processing apparatus which is provided with a magnet capable of forming a rotating magnetic field within the processing chamber. By adopting this structure, the electrons within the plasma can be trapped by the magnetic field formed inside the processing chamber so that the number of times they collide with the processing gas particles can be increased, thereby exciting a plasma of high density. In addition, by rotating the magnetic field, a high degree of uniformity in the density of the plasma can be achieved to realize uniformity, high speed plasma processing.
Now, it is crucial in a plasma processing process such as etching that the endpoint of the plasma processing be judged accurately to end the plasma processing with no delay. As a method for detecting the endpoint of plasma processing, a method in which any change in the light spectrum of a specific substance contained within the plasma in the processing chamber is detected, with the endpoint being detected based upon such change, has been proposed in the prior art. This method, which is conceived from the observation that the contents in the plasma change as the etching on the substrate progresses, aims to detect a real-time endpoint of the etching process accurately by monitoring change in the intensity of the light spectrum of a specific substance.
However, in the magnetic field assist type plasma processing apparatus described above, areas with varying degrees of density are formed within the plasma in correspondence to the direction of the magnetic field formed inside the processing chamber. Then, as the magnetic field rotates, the density distribution of the plasma also fluctuates. Consequently, it is necessary to take into consideration fluctuations of the plasma resulting from the rotation of the magnetic field when performing fixed-point observation of the plasma light through, for instance, a detection window provided at a wall of the processing chamber.
Accordingly, Japanese Unexamined Patent Publication No. H04 (1992)-338663, teaches for instance, a technology for achieving accurate endpoint detection by providing a rotary encoder that generates pulses in synchronization with the rotation of the magnet in an etching apparatus, sampling the plasma light in response to the pulses and removing the noise component brought by the rotation cycle of the magnet.
However, in a structure in which the plasma light is sampled in correspondence to the rotation cycle of the magnet, which is determined in hardware as described above, a device such as a rotary encoder must be added to the processing apparatus, resulting in a complicated apparatus configuration, and also in an increase in the initial cost of the apparatus.
In addition, in a structure in which the plasma light is sampled in correspondence to the rotation cycle of the magnet, which is determined in hardware as described above, the sampling cycle varies every time processing is performed. Moreover, in some cases, more efficient processing may be achieved by employing a fixed cycle as a sampling cycle in signal processing software for endpoint detection, and in other cases, a fixed cycle is absolutely required. Thus, there is a problem with the structure described above in that such requirements on the software side cannot be supported with a high degree of flexibility.